510 MOLLUSCA phylum vi 



Althougli tliis family is usually cliaracterised by a sinall smootli sliell, tlie essential 

 difference from tlie Dentaliidae is in the form of tlie foot. Typical forms of Gadulus 



appear in the Cretaceous ; the remaining 



A B c D genera are Tertiary and Recent. 



^|(-v f / Entalina Monts. Shell Dentalium-WkQf 



J|j||/S Ml largest at the apertnre, thence tapering to 



/nlj^ fl ^C\ %S ff *^^ ^"^^^ ' ^^^^^g^y ribbed, and angular in 



iM I ■ Im ^ tf section near tlie apex. Miocene to Recent. 



^ /l ^(^ hi Siphonodentalium Sars (Pulsellitm Stol. ; 



^^ SipJionentalis Sars). Shell an arcuate, 



Fig. 840. sliglitly taperiiig tube, circular in section 



A, Cadulus (Polyschides) denticulatus Desh. Cal- qj. nearly SO, and smooth externallv. Apex 



caire Grossier ; Damery, near Epernay. B, Cadulus '' ^ • ^^ ^•^ • ^ ^^ f ^ 



{DiscUdßs) hifissuratus Desh. Calcaire Grossier; rather large, typicaliy sllt mto lobes, but 



?oSN"oTteS,o.'''ASr.S™c. Tor.- sometime-s simple. Pliocene to Recent. 



tonian ; Monte Gibbio, near Sassuolo, Italy. Cadulus Phil. {Gadus Desh. ; Gadüa 



Gray; Heionyx Stimp.) (Fig. 840, G, D). 

 Shell tubulär, circular or oval in section, swollen near the middle or anteriorly, con- 

 tracting toward the apertnre. Cretaceous to Recent. 



Typical forms with simple anal orifice appear first in the Cretaceous, Dischides, 

 Jeffr. (Fig. 840, B), with two lateral slits, and Polyschides Pils. (Fig. 840, Ä), with 

 several notches, appear in the Eocene. All continue to the present time. 



Olass 3. AMPHINEURA von Ihering.i 



Aquatic, marine^ hilaterally symmetrical moUusks, with the head partially or not 

 differentiated ; in form worm-like with a ventral groove or none, or oval, flatternd, 

 with a foot adapted for creeping. Nervous System consisting of an oesophageal ring 

 with ganglia and four longitudinal cords, two ventral and two lateral ; no cephalic 

 eyes, tentacles, or otocysts. Gillspaired or many, posterior or lateral ; mouth anterior, 

 usually with a radula ; anus posterior, median. External surface with a series of 

 eight shelly plates, or stiffened tvith calcareous spicules. 



Order 1. APLACOPHORA von Ihering. 



Body vermiform, with a ventral groove, the skin elsewhere heset with calcareous 

 spicules ; no dorsal shelly plates in the adult. 



This is a degenei|ate group, represented in the Eecent fauna by about a 

 dozen genera belonging to two families — Chaetodermatidae and Neomeniidae. 

 Fossil remains are unknown. 



Order 2. POLYPLACOPHORA Blainville. Chitons. 



Amphineura protected by a dorsal series of eight shelly valves and an encircling 

 girdle ; with differentiated head, and a ventral sole or foot adapted to creeping ; gills 



^ Literature : Ihering, H. v. , Vergleichende Anatomie des Nervensystems und Phylogenie der 

 Mollusken, 1877.— Dali, W. H., On the Genera of Chitons. Proc. U.S. Nat. Museum, 1881, vol. 

 iv. — Hubrecht, A. A. W., A Contribution to the Morphology of the Amphineura. Quar. Journ. 

 Microscop. Soc, 1882, vol. xxii. [Bibliography, pp. 226, 227 .}— Hochebrune, A. T. de, Mono- 

 graphie des especes fossiles appartenant ä la classe des Polyplaxiphores. Ann. Sei. Geol. 1883, vol. 

 xiv. — Pruvot, Q., Sur l'organisation de quelques Neomeniens des cotes de France. Arch. Zool. 

 Exper. et Gener. [2], 1891, vol. ix. [Bibliography, pp. 702, 703.]— PiMry, H. A., Monograph of 

 the Polyplacophora. In Tryon and Pilsbry's Manual of Conchology, vols. xiv. and xv., 1892-93. 

 — Broili, F., Die Fauna der Pachycardientuffe der Seiser Alp. II. Scaphopoden und Gastropoden. 

 Palaeoutogr., 1907, vol. liv. 



